(a) Field of Invention
The present disclosure of invention relates to driving circuitry of a display device.
(b) Description of Related Art
In recent years, as a substitute for heavy and large cathode ray tubes (CRTs), flat panel displays, such as organic light emitting diode (OLED) displays, plasma display panels (PDPs), and liquid crystal displays (LCDs) have been actively developed.
The PDP is a device that can display characters and/or images by using a light-emitting plasma that is generated according to selective activation of a gas discharge. The OLED displays characters and/or images by using selective activation of field emission effects of particular organic materials or polymers. In the LCD, an electrical field is selectively applied to a liquid crystal layer interposed between two display panels, and transmittance of light passing through the liquid crystal layer is controlled by controlling strength of the electrical field to thus obtain a desired image.
So-called thin-film versions of these display devices (e.g. the LCD) include a display panel including a matrix of pixel units each having a switching element and a portion of a display signal line and a portion of a gate signal line passing through the pixel unit; where the latter gate signal line is driven by a multi-lines gate driver circuit that transmits gate-on voltage levels and gate-off voltage levels to selected ones of plural gate lines of the display in order to respectively turn on/off the corresponding switching elements of pixel units in selected display rows. A data driver is further provided to transmit data voltages to the data lines of the display so that the data voltages are applied to pixel-electrodes of the pixel units through the turned-on switching elements of a given display row.
In addition, in small and medium-sized display devices, there is a case where the gate driver is integrally formed on the display substrate using the same fabrication process as that used for the switching element in order to save costs in a large-sized display device.
The gate-lines driver typically includes a plurality of gate-line driving stages. The stages are often in a form where they combine to define a shift register that is arranged in a line adjacent to ends of rows of the pixel matrix. A moving row-select token or carry-signal is generated to move down the shift register and down the rows of the pixel matrix so as to select one row at a time. For example, a first shift stage transmits a logic “1” carry output signal to a next shift stage and so on, thereby sequentially generating a gate-activating output pulse, where the gate output pulse is synchronized to a scanning start signal.
In one class of embodiments, each shift register stage includes a plurality of MOSFET transistors, and some transistors among the plurality of transistors are operated to have same voltages at a gate and a source thereof when it is desired to turn the MOSFET off (render it nonconductive). However, even in such a case the amount of leakage current that flows through the supposedly-turned off transistor can be a significant amount for some specific applications. Accordingly, when excess leakage current flows, it may not be possible to maintain a desired constant voltage at the point where the leaking transistor is present and an output terminal controlled by the leaking transistor may not be appropriately operated, and the display screen may have a problem as a result.